Protection from penetration of a wall by debris in space or particle impacts caused by collision of a particle in space with the wall of a space vehicle is a particular concern which must be addressed by designers of space vehicles. This is particularly true of manned vehicles or structures such as the space station. The parameters for protection against orbital debris or impact particles have been defined in terms of the failure of an impacting particle to penetrate a wall where the impacting particle has a critical density or mass, a relative impact velocity and relative impact angle. For a given material and spherical particle shape, the critical density or mass can be expressed as a critical diameter.
"Whipple Shields" have been widely used in space operations and elsewhere for protection against penetration of a containment wall in hypervelocity micrometeroid environment and widely proposed for protection against recently developed man-made orbital debris environment. A Whipple Shield typically consists of two spaced apart sheets of metal where one of the sheets is a front "bumper" sheet with a separation spacing from a "back sheet" which can sometimes be a containment or rear wall (pressure hull). The material of the sheets, the thickness of the sheets, the density of the material and the density of the impacting debris, the velocity and the impact angle of the imparting debris and the spacing between sheets are some of the interrelated parameters which define the protection capability against penetration for a given Whipple Shield. As can be deduced, there are design trade offs, such as weight, volume and spacing for any given protection against a given impact particle of debris. Usually, the protection necessary is determined relative to a given impact particle which is defined in terms of critical diameter, velocity and impact angle. A Whipple Shield can then be designed with an optimum spacing between the bumper (outer wall) and back wall (inner wall) for selected bumper and back wall thickness of a selected material.
With no constraints as to weight, space, or prior design configuration, there are no problems in obtaining a Whipple Shield with suitable protection capabilities for the characteristics of any given impact particle. However, the fact is that weight, volume and space are critical parameters in space operations and existing design configurations are in place for some space vehicles. Thus, there is a need to improve performance levels of existing protection systems and/or systems with severe volume constraints without materially affecting existing structural design parameters.
In terms of function, the outer bumper sheet of a Whipple Shield is penetrated by an impact particle or object having mass, velocity and impact angle relative to the bumper surface. The impact on the wall of the bumper sheet shocks the impact particle converting some of the initial particle kinetic energy to thermal energy and produces smaller particle fragments to a size (critical diameter) where the fragments do not have sufficient energy (mass, velocity and angle of impact relative to the bumper surface) to individually penetrate the back containment wall. Additionally, in the space between the bumper sheet and the containment wall, the particle fragment cloud expands to impact a larger surface area of the containment wall, thereby eliminating concentrated energetic impact of the fragments on a single point on the wall, and increasing the penetration resistance of the wall.
In existing structures such as a space station, the structural design is quite intricate with many interrelated "trade-off" of parameters and the existing designs have a "Whipple Shield" for the crew area which is designed to provide protection against hypervelocity impact matter. With increasing concerns regarding protection against the accumulating orbital debris in space and its size, it is desirable to enhance the protection capability of existing Whipple Shields without requiring expensive redesign or without significantly increasing weight.